To improve the efficiency of thermally activated delayed fluorescence OLEDs by controlling the horizontal orientation through optimizing stereoscopic and linear structures of indolocarbazole isomers

Xiang, Songpo; Lv, Xialei; Sun, Shuaiqiang; Zhang, Qing; Huang, Zhi; Guo, Runda; Gu, Honggang; Liu, Shiyuan; Wang, Lei

doi:10.1039/c8tc01419a

Cited by 56 publications

(40 citation statements)

References 44 publications

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“…[37,38] Unexpectedly,i tw as observed that the emitting dipoles in these systemsa re partially aligneda nd that such anisotropic emission gives rise to al ight outcoupling factor.D evices with externalq uantum yields of > 30 %h ave been fabricated by using compound IndCzpTr-2 ( Figure 4). [39] However,t his process is not simplea nd, in fact, av ery recent finding from Durham University showedt hat the charge-transfer (CT) state must couple to al ocal (D or A) triplet state through spin-orbit coupling, and that the widely quoted idea of 1 CT-3 CT spinorbit coupling (SOC) interexchange is incorrect,b ecause it is a forbidden process. The ICT process of the excited molecules is affected by several environmental factors, including polarity, viscosity,a nd hydrogen-bonding interactions.…”

Section: Rtp and Df In Organic Emittersmentioning

confidence: 99%

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

Data

Takeda

2019

Chemistry An Asian Journal

156

121

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Organic emitting compounds that are based on π‐conjugated skeletons have emerged as promising next‐generation materials for application in optoelectronic devices. In this Minireview, recent advances in the development of organic emitters that irradiate room‐temperature phosphorescence and/or thermally activated delayed fluorescence with extraordinary luminescence properties, such as aggregation‐induced emission, mechanochromic luminescence, and circularly polarized luminescence, are discussed.

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Section: Rtp and Df In Organic Emittersmentioning

confidence: 99%

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

Data

Takeda

2019

Chemistry An Asian Journal

156

121

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“…CzTRZ (a = 0.34) is isotropically oriented while there is almost complete horizontal orientation in TCzTRZ (a = 0.05); DACT-II is preferentially horizontally aligned (a = 0.14), and the OLED employing this emitter reached an EQE max of 29.6%. Xiang et al and Maeng et al incorporated the more planar and rigid ICz (indolocarbazole) donor in Ind-CzpTr1 and IndCzpTr2, [11] and TRZ-TPDICz, [12] respectively, achieving high EQE max values of 14.5%, 30%, and 30.3%, respectively, due in part to the preferential horizontal orientation of these emitters. Indolocarbazole has been previously employed in TADF emitter design as the donor moiety in a small number of reports, although none of these cases showed a di-functionalized ICz unit.…”

Section: Introductionmentioning

confidence: 99%

“…[6,17] By adding a second acceptor onto the ICz donor, this should lead to an increased HOMO-LUMO gap and a blue-shifted emission than the previously published mono-functionalized emitters employing the ICz moiety. [11,12,18] Indeed, ICzTRZ shows both very high photoluminescence quantum yield and strongly horizontally oriented transition dipole moments (TDMs) and demonstrates its potential in a highly efficient sky-blue OLED.…”

Section: Introductionmentioning

confidence: 99%

“…and Maeng et al. incorporated the more planar and rigid ICz (indolocarbazole) donor in IndCzpTr1 and IndCzpTr2, [ 11 ] and TRZ‐TPDICz, [ 12 ] respectively, achieving high EQE max values of 14.5%, 30%, and 30.3%, respectively, due in part to the preferential horizontal orientation of these emitters. Indolocarbazole has been previously employed in TADF emitter design as the donor moiety in a small number of reports, although none of these cases showed a di‐functionalized ICz unit.…”

Section: Introductionmentioning

confidence: 99%

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Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Zhang

Crovini

Santos

et al. 2020

Advanced Optical Materials

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employing a purely organic TADF emitter, 4CzIPN. [3] TADF molecules have an energy gap between the S 1 and T 1 states, ΔE ST , sufficiently small to allow the triplet excitons to convert into singlet excitons through reverse intersystem crossing (RISC), making possible their radiative decay from the singlet excited state, evidenced by a delayed fluorescence. To minimize ΔE ST and enhance k RISC , the overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the molecule must likewise be small, which is achievable in compounds containing electron-donating and electron-accepting moieties that are poorly electronically coupled giving the excited state an intra-molecular charge-transfer (CT) character. [4] The most common emitter designs rely on a large twist angle between the donor and acceptor coupled with the incorporation of aromatic spacer bridging moieties. [5] The external quantum efficiency (EQE) of the OLED is a function not only of the IQE but also of the light out-coupling efficiency. As the stack of an OLED device is composed of several different layers of materials included between two electrodes, total internal reflection at the interface between two media, and coupling to surface plasmon polaritons (SPP) at the interface with Organic thermally activated delayed fluorescent (TADF) materials can harvest 100% of the electrically generated excitons as a result of their small singlet-triplet energy difference. However, maximizing the external quantum efficiency (EQE) of a device also requires enhancing the light out-coupling efficiency. This work presents a new acceptor-donor-acceptor (ADA) emitter employing an indolocarbazole donor and diphenyltriazine acceptors that show nearly-completely horizontal orientation regardless of the host matrix, leading to a sky-blue organic light-emitting diode (λ EL = 483 nm, CIE coordinates of 0.17, 0.32) with EQE MAX of 22.1%, a maximum luminance of 7800 cd m −2 , and blue emission.

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“…[ 22 ] This experiment demonstrated the benefits of the rigid donor structure along with other works about rigid donors based on carbazole. [ 23–25 ] However, the lifetime and efficiency roll‐off of the TADF devices were not satisfactory, which requires the design and development of the even stronger donor than the benzofurocarbazole.…”

Section: Introductionmentioning

confidence: 99%

Starburst Type Benzofuroindolocarbazole Donor for High Efficiency and Long Lifetime in Thermally Activated Delayed Fluorescence Emitters

Kim

Yoon

Lee

et al. 2020

Advanced Optical Materials

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In many TADF materials, the general molecular structure was a donor-acceptor type structure in order to have a small singlet-triplet energy gap (ΔE ST) value by minimizing the orbital overlap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) for effective RISC. To date, a lot of TADF materials that feature donor-acceptor structure have been reported by managing the donor and acceptor units, which indicate that the selection of donor and acceptor moieties plays an important role in the TADF emitters. In many papers, the electron acceptors such as diphenyltriazine, diphenylsulphone, pyridine, pyrimidine, etc., have been reported. [5-8] Whereas, the electron donors have been rather limited as acridine, carbazole, and phenothiazine derivatives. [1,8-20] Therefore, the development of new electron donors is urgently necessary. Particularly, it is important to develop a donor with a rigid structure because the use of rigid donor moiety was effective to improve EQE and reduce efficiency roll-off at high luminance. [21] We have already demonstrated that a carbazole derived benzofurocarbazole donor allowed improved TADF performances by the rigidity and strong donor character. [22] This experiment demonstrated the benefits of the rigid donor structure along with other works about rigid donors based on carbazole. [23-25] However, the lifetime and efficiency roll-off of the TADF devices were not satisfactory, which requires the design and development of the even stronger donor than the benzofurocarbazole. In this work, we developed a starburst type rigid donor, benzofuro[3,2-a]indolo[3,2-c]carbazole (Trx), as the donor of the TADF emitters, and two isomeric TADF emitters, 5-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-(15-phenylbenzofuro[3,2-a] indolo[3,2-c]carbazol-10(15H)-yl)benzonitrile (TrzCNTrx1) and 5-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-(10-phenylbenzofuro[3,2-a] indolo[3,2-c]carbazol-15(10H)-yl)benzonitrile (TrzCNTrx2), were synthesized. The Trx was developed as a rigid and strong electron donor for strong charge transfer character in the TADF emitters in combination with a diphenyltriazine electron acceptor and a benzonitrile linker. Thus, the TrzCNTrx1 and TrzCNTrx2 emitters showed a small ΔE ST , high photoluminescence quantum yield, and short exciton lifetimes. In the device application, the

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To improve the efficiency of thermally activated delayed fluorescence OLEDs by controlling the horizontal orientation through optimizing stereoscopic and linear structures of indolocarbazole isomers

Abstract: By optimizing linear and stereoscopic structure of emitter to obtain preferential horizontal orientation, a high EQE green device of 30.0% based on IndCzpTr-2 was realized.

Cited by 56 publications

References 44 publications

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Starburst Type Benzofuroindolocarbazole Donor for High Efficiency and Long Lifetime in Thermally Activated Delayed Fluorescence Emitters

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